Custom domain won't save when I click "Add"

Hello. I am trying to map a custom domain to a user's blog and it won't save when I click "Add"... it just disappears. However, when I add one to my default blog, it works.

My guess is that I have installed the plugin incorrectly, however, I followed the instructions... they just seem incomplete. For example, the official installation instructions say nothing about uploading the /domain_mapping/ directory (which includes the /languages/ directory) anywhere. Instead, it simply says to upload the domain_mapping.php file to the /mu-plugins/ directory.

Additionally, I went into phpMyAdmin to see if the wp_domain_mapping table was being created (Note: I do not use the default wp_ prefix - Hopefully, that doesn't matter) and it is there. However, I also noticed that the table's collation column displays "latin1_swedish_ci" instead of "utf8_general_ci". Does this matter? I also noticed that my supporter tables displayed the same.

In any case, I'm hoping you can help me out with this.

My website, is hosted with I have a dedicated IP assigned to it. I have installed the Supporter plugin, Domain Mapping plugin, and now the Multi-Domains plugin hoping to rectify the situation as it appears all three are plugins are designed to work together.

Please advise.